Method for sterilizing a drink supply pipe line (7) for supplying a sterilized drink from a heat-sterilizing unit (18) into a filling machine (2), wherein an upstream side circulation path (6a) is formed by forming an upstream side return path to an upstream side pipe line section (7a) passing through the sterilizing unit of the drink supply pipe line, a downstream side circulation path (6b) is formed by forming a downstream side return path to an downstream side pipe line section (7b) of the drink supply pipe line extending from a downstream side portion of the upstream side pipe line section to the filling machine, an alkaline cleaning liquid is circulated within the upstream side circulation path and the downstream side circulation path to thereby clean and sterilize an interior of the drink supplying pipe line, and a drink filling working is started after performing a rinsing treatment with water.
